On the Equilibrium of Heterogeneous Substances

J. Willard Gibbs's work, particularly his 1876 paper "On the Equilibrium of Heterogeneous Substances," laid the foundation for understanding thermodynamic equilibrium. He developed the phase rule, which relates the number of phases (P), chemical components (C), and degrees of freedom (F) in a system at equilibrium using the formula F = C - P + 2. This rule helps predict how temperature, pressure, and composition affect different states of matter (solid, liquid, gas) within a system. Gibbs's work transformed physical chemistry into a deductive science. His contributions also include the development of thermodynamic potentials like Gibbs free energy, crucial for analyzing open systems.123